As a data storing method of a network system, file systems, such as a network file system (NFS) or a common Internet file system (CIFS), are known. A file server provides functions as such file systems by executing a server program of the NFS or the CIFS.
In a case where such file systems are used through an external network, an account and a password are commonly used as an authentication key.
Patent Literature 1: JP 2003-044225 A
Patent Literature 2: JP 2002-524793 A
Patent Literature 3: and JP 2007-073004 A
However, in such a network system of the related art, if information of the account and the password leaks out, an unauthorized access may be performed by spoofing of the third party, causing the occurrence of data leakage.